Liquid crystal displays are widely used as displays for TVs and computers due to its advantages of light weight, low irradiation and portability.
A liquid crystal display includes various modes such as In-Plane Switching (IPS) liquid crystal panel and Fringe-Field Switching (FFS) liquid crystal panel. A liquid crystal panel includes an array substrate, a color filter substrate and a liquid crystal layer encapsulated between the array substrate and the color filter substrate. FIG. 1 is a structural representation of an array substrate in an IPS liquid crystal panel of prior art. As illustrated in FIG. 1, the array substrate in an IPS liquid crystal panel in the art of state includes a substrate (not illustrated in the figure), gate lines 101, data lines 102, pixel electrodes 103, common electrodes 104, common electrode lines 105 and thin film transistors (TFTs); and the sources and drains of the TFTs are connected with the data lines 102 and pixel electrodes 103 respectively, the gates of the TFTs are connected with the gate lines (or scan lines) 101 respectively, and the common electrodes 104 are connected with the common electrode lines 105. Turning on or off of the TFTs is controlled by gate drivers in the liquid crystal panel. When a TFT is turned on, a data signal, which is an alternating voltage, is applied onto a pixel electrode 103 through a source driver, and a constant voltage Vcom is applied onto a common electrode 104. The constant voltage Vcom is of a value between a high potential in a positive period and a low potential in a negative period of the alternating voltage applied onto the pixel electrode 103 to form an electric field, between the pixel electrode 103 and the common electrode 104, that can control alignment direction of liquid crystal molecules in the liquid crystal layer. The constant voltage is generally of an intermediate value between the high potential in the positive period and the low potential in the negative period of the alternating voltage.
FIG. 2 is a voltage signal diagram on a pixel electrode and a common electrode in the art of state. As illustrated in FIG. 2, in the figure, Vg denotes a scan signal output from the gate driver, Vp denotes an actual alternating voltage on the pixel electrode 103, Vp′ denotes an object alternating voltage applied onto the pixel electrode 103, where ΔVp=Vp′−Vp. In the art of state, when a gate driver in the liquid crystal panel turns on the TFT connected with a pixel electrode 103, a source driver in the liquid crystal panel applies an alternating voltage to the pixel electrode 103, that is, charges the pixel electrode 103. Since the TFT in the array substrate further includes some parasitic capacitance, the source driver will charge these parasitic capacitors at the same time, which will generate coupling capacitance. When the gate driver in the liquid crystal panel turns off the TFT connected with the pixel electrode 103, the source driver stops charging the pixel electrode 103. The gate driver causes the voltage drop (typically 30˜40V) generated when the TFT is turned off to be fed back to the pixel electrode 103 through the coupling capacitance, resulting in a voltage drop of ΔVp on the pixel electrode 103. Since the voltage applied onto the common electrode 104 is a constant voltage, but there will be a voltage drop of ΔVp on the pixel electrode 103 both in a positive period and a negative period of the alternating voltage, the voltage value on the pixel electrode 103 become non-symmetric with respect to the constant voltage applied onto the common electrode 104, thereby influencing the gray scale values of the displayed image, leading to image retention. Meanwhile, some charged ions remain in the liquid crystal layer during the fabrication of a liquid crystal panel, which will accumulate nearby an alignment layer under the effect of an electric field, thus when the liquid crystal panel displays the next frame image, the electric field in the liquid crystal layer will change, while the electric field generated by residuary charged ions in the liquid crystal layer cannot be rapidly changed accordingly. The electric field generated by residuary charged ions causes the liquid crystal panel to display the previous frame of image still, resulting in even severer image retention.